The invention disclosed herein relates generally to arrangements for mounting key caps in key switch apparatus, and more particularly to a key cap and support column configuration which permits mounting of the cap in either of two angular relationships relative to the column to provide for either a sloped or a stepped keyboard configuration using the same parts.
Manual keyboards, such as used in office machines, computer terminals and other manually controlled electronic installations are commonly produced in either sloped or stepped configurations. In either configuration, an array of key switches is mounted on a panel which is inclined relative to horizontal. In the sloped configuration, the top surfaces of the key caps are generally parallel with the supporting panel and define a plane parallel therewith. In the stepped configuration, the plane defined by the top surface of each key cap is at an angle with respect to the supporting panel. The angle may be equal and opposite to the angle of inclination of the panel so that the key tops are horizontal, and the rows of key tops are in tiers or steps.
The selection of a keyboard configuration depends both on application requirements and predominant operator preference. However, aside from the particular geometry, the keyboards and switches used therein contain the same basic functional elements. Manufacturers of key switches and keyboards must normally be able to supply parts and assemblies for either keyboard configuration. Of course, this can be accomplished by utilizing different sets of key caps and associated plungers or columns for each configuration. However, such an approach requires duplication of inventory and manufacturing effort.
One technique utilized to avoid such duplication has been to provide key caps and associated support columns with two sets of mating surfaces so that the caps and columns can be assembled in either of two angular relationships. U.S. Pat. No. 3,667,787 issued to N. Semour on June 6, 1972 shows such an arrangement. As disclosed in the patent, the key cap contains a recess having one set of surfaces which is perpendicular to the upper surface of the cap and a second set of surfaces which is inclined with respect to surfaces in the first set by an angle equal to a desired key top angle. The support column or post is formed with complimentary mating surfaces, some of which are parallel with a longitudinal axis of the post and some of which are inclined with respect to the longitudinal axis.
At least some of the mating surfaces are paired in different ways to establish the two different angular relationships. Assembly in one relationship predominantly utilizes parallel exterior surfaces on the post and complimentary interior surfaces in the cap. Assembly in the other relationship in which the post and cap are rotated 180.degree. relative to one another utilizes surfaces in planes inclined toward one another on the post and corresponding inclined surfaces in the cap. Where parallel surfaces are used, a secure friction fit between the cap and post can be easily achieved. This relationship minimizes any tendency for the cap to "walk off" the post with use.
The previously described arrangement requires a somewhat complex geometry for the recess in the key cap and mating areas on the top of the support post. If the elements are molded from a thermosetting plastic or other similar material, manufacturing of the molds and the subsequent molding process are correspondingly complicated. More complicated forms generally dictate maintenance of closer tolerance control, and result in poor tolerance control having greater effect on fit. Another characteristic of having two at least partially independent sets of mating surfaces is that not all of the surfaces can be in contact so as to be load bearing in alternative configurations. In general, it is preferable to maximize the load bearing area so as to minimize stresses in the material.
The applicant has provided a unique key cap mounting arrangement adapted for either of two angular orientations in which the same set of parallel mating surfaces on the key cap and corresponding surfaces on the support column are used for either orientation. Since the mating surfaces are parallel for both orientations, there is no tendency for the cap to "walk off" the column with use. The form required for the mating surfaces is exceptionally simple, thus minimizing the complexity of forming molds and the molding process, and minimizing sensitivity to dimensional tolerances.